examples: beware of intl portability issues

Reported by Horst von Brand.
https://lists.gnu.org/r/bug-bison/2020-04/msg00033.html

* examples/c/bistromathic/Makefile: libintl might not be needed, but
libm probably is.
* examples/c/bistromathic/parse.y: Include locale.h.

examples/c/bistromathic/Makefile

@@ -5,7 +5,7 @@ BASE = bistromathic
 BISON = bison
 XSLTPROC = xsltproc
 
-# We need to find the headers and libs for readline and intl.
+# We need to find the headers and libs for readline (and possibly intl).
 # You probably need to customize this for your own environment.
 CPPFLAGS = -I/opt/local/include
 LDFLAGS = -L/opt/local/lib
@@ -14,7 +14,7 @@ LDFLAGS = -L/opt/local/lib
 BISON_LOCALEDIR = $(shell $(BISON) $(BISON_FLAGS) --print-localedir)
 CPPFLAGS += -DENABLE_NLS -DBISON_LOCALEDIR='"$(BISON_LOCALEDIR)"'
 
-LIBS = -lreadline -lintl
+LIBS = -lreadline -lm # In some environments, -lintl is needed.
 
 all: $(BASE)
 

examples/c/bistromathic/parse.y

@@ -2,6 +2,7 @@
 
 %code top {
   #include <ctype.h>  // isdigit
+  #include <locale.h> // LC_ALL
   #include <math.h>   // cos, sin, etc.
   #include <stdarg.h> // va_start
   #include <stdio.h>  // printf